Currently, application of a composite film in display and illumination will be a new direction for future display and illumination technologies. It is well known that white light is obtained by a combination of colors such as red, green, blue and yellow, and typically, respective colors are achieved by their respective corresponding light-emitting materials, which can achieve white light by co-doping.
In recent years, a new type of semiconductor nano-material—quantum dots—emerges, which is also known as a semiconductor nano-crystal, with a size between 1-10 nm. Due to a quantum size effect and a dielectric confinement effect, the quantum dots have unique photo-luminescent and electroluminescent properties. As compared with conventional organic fluorescent dyes, the quantum dots have superior optical characteristics such as high quantum efficiency, high photochemical stability, not prone to photolysis, and broad excitation, narrow emission, high color purity, and having luminous colors adjustable by controlling the size of the quantum dots. Thus, white light is often achieved by using the quantum dots in the prior art. There is a film emitting white light, which is obtained by mixing the quantum dots of a plurality of different colors; however, at the time of achieving white light, phenomena such as agglomeration and fluorescence quenching are apt to occur between the quantum dots.